1. Field of the Invention
The present invention relates to a finder optical system of a camera, and more particularly to an Albada finder optical system of inverted Galilean type which comprises, from the object side, a front lens group of a negative refractive power and a rear lens group of a positive refractive power, and which is capable of indicating marks, such as a frame a distance indicator and so on, in a finder field.
2. Description of the Prior Art
The above type finder optical systems are known which comprises a front lens group consisting of two negative lens components and a rear lens group consisting of one positive lens component, by Japanese Laid-Open Patent Application Nos. 50-27539, 59-33419, 59-23330 and so on. Such construction is shown in FIG. 1. In FIG. 1, a virtual image of an object is formed by a first negative lens component (Lo.sub.1) and a second negative lens component (Lo.sub.2), and the virtual image is magnified by a third positive lens component (Le) for finder observation. A frame mark (M) for indicating a frame in finder field is formed on a glass plate (P) located between the second and third lens components (Lo.sub.2)(Le). The eye side surface of the second lens component (Lo.sub.2) is a reflecting surface for reflecting the light from the mark (M) towards the eye. Thus, an image of the mark (M) is indicated in the finder field. In this construction, the distortion is controlled by dividing a negative refractive power into two lens components.
On the other hand, an inverted Galilean type finder optical system having no indication by Albada type optical system is shown in FIG. 2. In FIG. 2, the inverted Galilean type finder optical system comprises, from the object side, an objective lens group consisting of a negative objective lens component, and an eyepiece lens group consisting of a positive eyepiece lens component.
Here, it is clear that the Albada finder lens system of inverted Galilean type shown in FIG. 1 is more complex in construction than the inverted Galilean finder lens system shown in FIG. 2 is. Therefore, the Albada finder lens system is complex in manufacturing and in adjustment of each elements, and causes to require more cost.